the coking properties of coal at elevated pressures. - Argonne ...

It has been recognized by many researchers that although ash fusion tests can
given useful information regarding the fouling and slagging propensities of coal ashes,
there are serious shortcomings. First, the tests are based on subjective observations
and not precise scientific measurements, and they have a large margin of error. For
example, the ASTM-method which is widely used in many countries allows for a 55 K
margin of reproducibility in the initial deformation, softening hemisphere temperatures
in an oxidizing atmosphere, and a 70 K margin of uncertainty in determining the initial
deformation temperature in a reducing atmosphere.
Within that 70 K margin the viscosity
can change by an order of magnitude and consequently the rate of ash sintering will
change by the same factor.
Another, more serious, shortcoming with the ash fusion method is that when testing
some coal ashes there occurs an extensive degree of particle-to-particle bonding without
any visible sign of deformation in the shape of an ash pellet. It is, therefore, evident
that an additional method is needed to assess the sintering characteristics of coal
ashes. A choice of sinter measuring techniques is given in Table 2.
TABLE 2. REVIEW OF ASH SINTERING TECHNIQUES
Measuring Technique Equipment
Neck-growth measurements between A furnace and a
spherical particles (Kuczynski, microscope
1949), Raask, 1973)
Simultaneous shrinkage and
electrical conductance
measurements (Raask, 1979)
Needs a purpose-built
furnace assembly for
more accurate measure-
ments. A simpler
version uses platinum
wire electrodes as
described by Raask
(1979) and by Cumming
(1980)
Crushing strength measure-
A furnace and a
ments of sintered ash
crushing strength
pellets (Atting and
Barnhard, 1963; Gibb, 1981)
measuring device
Ash agglomeration by
sieving test (Stallman
and Neavel (1980)
Ash plug flow method
A furnace and a
sieving machine
A tubular furnace tube
with perforated plate
to support an ash plug
Comments
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This is suitable for
homogeneous material when
available in the form of
spherical particles. It is
not suitable for routine
sinter testing of coal ashes.
Each ash could be provided with
sintering rate curves. The
method needs to be tested and
assessed by different
researchers,
The method has been used by
several researchers but there
is no agreed procedure
This is one of the simplest
methods of testing for
initial sintering, and it
warrants more systematic
tests
So far no experimental results
have been found in
1 i terature
The brief review in Table 2 shows that there are several laboratory methods of
sinter testing coal ashes, which can give some useful information regarding their deposit
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